Electric motor.



B. F. W. ALEXANDERSON.

ELECTRIC MOTOR.-

APPLICATION FILED MAR.1, 1907.

923,31 1. Patented June 1. 1909.

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WHfryesses: Inventor m I Ernst FWAlexandzrsgm y um mm by NORRIS FEYERS, "(C LIYHQ. WASMXNGTON. Dv C E. P. W. ALEXANDERSON.

ELECTRIC MOTOR. APPLIOATION FILED MAR. 1, 1907.

Patented Julie 1, 1909.

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lnvenkor Ernst FWAIzxandzrson, r by M WVCnesses NORRIS PETERS, INC.. LITHO. WASHINGTUN Dv C E. P. W. ALEXANDERSON.

ELECTRIC MOTOR.

3 SHEETS-SHEET 3 Witnesses:

Inventor:

Ernst F. W. JI lexanderson UNITED STATES QT Enron ERNST F. W. ALEXANDERSON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- I TRIO COMPANY, A CORPORATION OF N'EW YORK.

ELECTRIC MOTOR.

Application filed March 1, 1907. Serial No. 859,957.

. To all wi'wm it may concern:

Be it knownthat I, ERNST F. W. ALEX- ANDERSON, a citizen of the United States,

lgs'iding at Schenectady,'county of Schenec- I s y State of New York, have invented certam new and useful Improvements inElectrie Motors, of which the following is a speci-' fication. inventlon relates to compensated electric motors of the commutator type, and is particularly applicable to alternating-current compensated series motors; though in its broader aspect it is not limited to alternat lug-current motors, nor to a series connec and efficiency, and, owing to the special difficulties in commutation in alternating-current motors, the production of acommutating field is highly desirable. By my invention 1 am enabled to obtain both these results without the necessity'of a commutating pole or compensating winding in the interpolar space. I secure this result by winding the armature with a fractional pitch approximately equal to the width of the pole face. With such an arrangement the currents in the coil conductors on that po'rtion of the armature which is at any instant opposite the polar space neutralize each other, since, owing to the fractional pitch, the currents in half the conductors in each slot in this portion of the armature, are flowing in the oposite direction to. the currents in the other alf. Consequently the only portions of the armature which require com ensation are those whichdie opposite the eld po les, so that a compensating winding distributed over the pole faces only is sufficlent for perfect com ensation. Furthermore, on account of t e coil-width selected for the armature, each coil short-circuited by a commutator brush is just passing the tipsof the pole, so that if a commutatmg field is produced. at the pole tips, it Is at the proper posi- Specification 01 Letters Patent.

Patented June 1, 1909.

tion. Such a field at the pole tips may readily be produced. In a direct-current motor it is sufiicient merely to design the compensating winding to over-compensate the armature reaction, while in an alternating-current motor, in which the phase of the coinmutating field should differ from that of the main field, the desired commutating field may be secured in a simple manner, as will be hereinafter explained.

My invention will best be understood by reference to the accompanying drawings, in which-.

Figure 1 shows diagrammatically a com pensated motor arranged in accordance with my invention Fig. 2 shows the connection of the windings for a series motor; Figs. 3- and a show modifications for securing the proper phase of commutating field for an alternating-current motor Fig. 5 shows diagrammatically a development on a plane surface of thestator windings arranged as in Fig. 4, Fig. 6 shows a development on a plane surface of the armature windings and Fig. 7 is a diagram of the connections of the windings arranged as in Fig. 3.

In F l A represents the field structure,

which for an alternating-current motor, is

laminated. This field structure is provided with polar projections between which are mounted the main field coils B. O represents the compensating winding, the coils of which are each indicated diagrammatically by a single line. D represents the armature, E the commutator, and as the commutator brushes. The armature coils have a fractional pitch, the width of each coil being ap proximately equal to or a little less than the breadth of a pole face. The effect of the fractional-pitch winding is, as is well understood in the art, to produce in a certain portion of the armature a neutralization of the magnetizing efi'ect of the current in one coil by the current in another coil in thesame slot. With the breadth of coil shown in Fig. 1, this neutralization occurs in all the slots opposite the interpolar space of the field, so that only the coil conductors opposite the pole faces are effective-in producing magnetization. Consequently the compensating winding shown, although it is distributed over the pole faces only, is sufficient for producing perfect compensation. The eiiect of the fractional pitch on current distribution. and distribution of magnetomotive force is best shown in Fig". 6,:where the di rections of current at an'yinstant in each armature coil are shown by arrow-heads, and

this figure, taken in connection with Fig. 5,

shows the relation of the armature currents .to the fieldoles and currents'in the comtips, it will be in pro pensating w riding.

The connections of armature, compensating winding, and field, for a series motor are shown diagrammatically in Fig. 2.

From an inspection of Fig. 1, and of Figs."

5 and 6 it will be seen that the coils which are short-CirCuited by thecommutatorbrushes are just approaching orl'eaving the Consequently, if a flux of propernatingcurrent motor, of the proper phase.

This 'commutating field in an alternatingcur'ren't motor should not be'in phase with the main current, but should: be displaced therefrom, as is well understood in the art,

the special coils F a so that the conductors of the compensating winding C, which are in the main motor circuit, would not alone produce a commutat- By employing ing field of the proper phase.

flux of any desired phase may be produced at the pole tips by supplyitg current of the proper phase and amount to these coils. The desired phase of the current in the coils F rnay be obtained by any suitable connection, as, 'IOI instance, by a shunt-connection, shown in Fig. 7.

' Inplace of using special coils for the commutating field, the same result-may be obtained by shifting the phase'of the current in the conductors of the compensated winding Such an ar- In these figures the two coils of the compensating winding, which lie in the'slots nearest the pole tips, are shunted by an impedance G,

which isproportioned with the proper in1 pedance-fa ctorsifor' securing the desired current phase in the conductors of the compensating winding which it shunts. A non-1nductiveresistance, such as is indicated in the drawing, is adapted for this purpose, since it serves to lag the phase of the current in the coils of the compensating winding which it shunts. i

It will be understood that-I have illustrated my invention diagrammatically, and thatin practice windings and motor construction 'may be em loyed.

Fhat I claim as new and desire to secure by Letters Patent of the United States, is,- 1'.- In. a dynamo-electric machine, a .field any well-known form of magnet having polar-projections, main field coils carried in the interpol'ar spaces,- a comensating winding distributed on the pole faces, an armature provided with a commue tator, and armature coils having a fractional pitch equal to the breadth of the 'pole faces. f :2. In a dynamo-electric machine, an armature provided with a commutator and a fractional pitch'winding, a laminated field structure, a compensating winding .distributed over a'portion only of the field correspondingto the pitch of the armature coils, and magnetizing coils occupying the portion of the field magnet not occupied by the com ,pensati ng winding.

-3. Infla dynamolectric machine, a laminated field-magnet having polar projections, main field coils carried in the interpolar spaces, a compensating winding distributed on the pole faces, an armature provided with a commutator, armature coils having a frac-. tional pitch equal to the breadth of the pole faces, and means for producing a commutating field at'the pole tips. l

4', In a dynamo-electric -machine, an armature provided with a cornin-utatorand a fractional pitch winding, a laminatedfieid structure, a compensatin winding distributed "over a'portion only of the field corre-' sponding'to the pitch of the armature coils, magnetizing coils occupying the portion of the field magnet not occupied by the compensating winding, commutator brushes, and means for producing a commutating field at the points occupied by the coils which at any instant are short-circuited by the brushes;

5. In an alternating '-current motor, a laminated stator having polar projections, magnetizing coils carriedinthe interpolar spaces, a winding distributed on the pole faces, a rotor provided with a commutator. and brushes, rotor coils havin a fractional pitch equal to the breadth of the pole faces,- and means for shifting the phase of the flux at the tips of the poles with respect to the flux 'over' the rest of the pole face. 6'. In. an alternating-current motor.,' a laminated stator having polar projections, magnetizing coils carried in theinterpolar spaces, a Winding distributed on the pole faces, a rotor provided with commutator and brushes, rotor coils having a fractional pitch equal to the breadth of the ole faces, and an impedance connected in s unt to the conductors of the Winding distributed on'the pole-faces which lie at thetips of the poles.

In witness whereof, I have hereunto set my 120 hand this 26th day of February, 1907.

ERNST r. W.- ALEXANDERSON. Witnesses: I BENJAMIN B. -HU L, v HE EN ORFORD. 

